In the prior art, there has been proposed (as referred to in Patent Publication 1, (JP-A-2001-121500) for example) a semiconductor dynamic quantity sensor formed by a semiconductor layer supported over a supporting substrate and which includes moving parts to be displaced in a predetermined direction over the supporting substrate, and a beam portion for connecting the supporting substrate and the moving part. The sensor detects a dynamic quantity based on the displacement of the moving parts.
FIG. 6 is a diagram showing a top plan view of a beam portion 50 in a prior art semiconductor dynamic quantity sensor described in Patent Publication 1.
In the beam portion 50 shown in FIG. 6, three beams 51, 52 and 53 are arranged in parallel and connected together by a connecting portion 55 at first end portions. The beam portion 50 bends in a direction X perpendicular to the longitudinal direction Y of the beams 51, 52 and 53.
Here, in the beam portion 50 of the prior art, the two outer beams 51 and 52 of the three beams 51, 52 and 53 have an equal length, and the other end portions of these two outer beams 51 and 52, i.e., the end portions on the side opposed to the connecting portion 55, are fixed to the supporting substrate by a fixing portion 56.
Moreover, in the beam portion 50 of the prior art, a moving part 30 is connected to the other end portion of the central one 53 of the three beams 51, 52 and 53 and not connected to the two outer side beams 51 and 52. Motion of the beam portion 50 in an unnecessary direction is minimized by adopting such a shape of the beam portion 50.
In short, in this beam portion 50, the predetermined direction for the moving part 30 to be displaced is the aforementioned direction X. Further, there is a proportional relationship between the displacement of the moving part 30 in the predetermined direction X and the mass of the moving part 30.
However, according to the inventor's investigations, it has been found that even when the prior art construction of the beam portion 30 is adopted, depending on the size relationship between the width B of the connecting portion 55 and the thickness A of the connecting portion 55, the beam portion 50 will still bend in an unnecessary direction. The thickness A is taken in the longitudinal direction Y of the beam portions 51 to 53. The width B is taken in the direction X perpendicular to the longitudinal direction Y of the beams 51 to 53.
For example, assume a case in which the connecting portion 55 of the beam portion 50 bends in the longitudinal direction Y of the beams 51 to 53, as indicated by broken lines in FIG. 6. Then, the moving part 30 is displaced not only in the predetermined direction X for its displacement but also in the aforementioned longitudinal direction Y, i.e., the unnecessary direction.